Immunostaining with antibodies against protein kinase C isoforms in the fovea of the monkey retina

Abstract

We reported previously that an antibody to the alpha isoform of protein kinase C (PKC) immunostained rod bipolar cells and bipolar cells that could be blue-cone (B-cone)-specific in postmortem human retina (Kolb et al. (1993) Vis. Neurosci. 10:341-351). In addition, we showed that antibodies to the beta isoform of PKC immunostained cone system bipolar, amacrine, and ganglion cells. Since the fixation of the human material was poor, we were unable to make positive identifications of the specific cell types that were immunoreactive, particularly in the case of PKC-beta antibodies. Thus, herein we have repeated the study on well-fixed monkey foveal retina. PKC-alpha immunoreactivity (IR) was restricted to a single type of cone bipolar cell that contacted only a minority of the cone pedicles at central invaginating contacts of ribbon triads. This bipolar type shares some morphological characteristics of B-cone-specific bipolar cells of primate retina. PKC-beta immunoreactivity was found in cone bipolar cells that made primarily basal contacts with cone pedicles and had axon terminals in sublamina alpha of the inner plexiform layer (IPL). Immunoreactivity also occurred in a type of cone bipolar that made central element contacts and had axon terminals in sublamina b of the IPL. Some ganglion cells, particularly those postsynaptic to flat midget bipolar cells also exhibited PKC-beta-IR. One type of amacrine with an 8 microns diameter cell body showed strong PKC-beta-IR. It was postsynaptic to cone bipolar cells in both sublamina a and b and presynaptic to bipolar axons, other immunoreactive amacrine cells, and ganglion cell dendrites and bodies. The other amacrine cell type showed less strong PKC-beta-IR, large-bodied (12-15 microns cell body diameter), and probably diffuse in branching pattern. The latter interacted with the intensely immunoreactive amacrines, bipolars, and ganglion cells. By comparison to cat and primate retinas where morphology and physiology of many retinal neurons are well documented, we suggest that PKC-beta may be specific to flat midget, flat diffuse, and invaginating diffuse cone bipolar cells and to at least two amacrine cells. Some of these neural types are proposed to be involved in OFF-center cone pathways in the monkey retina.